In biological research or diagnosis in medicine, it is often required to dissociate a sample, such as tissue, into isolated cells. Tissue dissociation is often achieved by enzymatic digestions and/or mechanical dissection using fragmentation devices, for example as disclosed in European Patent EP1843852 B1. In the case of dissociation, the single-cells are separated from dissociated tissue fragments by filtration.
Filter systems for biological research or diagnosis in medicine are long known. Gauze was initially used for separating isolated cells from bigger particles or tissue. As gauze absorbs the liquid of the sample in part, so called cell strainers having a mesh for filtration are used for this purpose. Cells strainers are available in several mesh sizes depending on the particles to be separated, for example on the size of the target cells.
Since the most common laboratory vessels for biological research or in medical diagnosis (testing) are so called tubes (also called “test tubes”), i.e. small cylindrical-shaped vessels with a flip or screw cap, it is desired to perform the filtration into such tubes without the need for further handling of the sample. Such tubes are available for several different volumes, thereby having different sized openings. For researchers working with cells, especially 15 ml and 50 ml volume are common tube formats.
Commercially available cell strainers for laboratory use are disposable, sterile packed and available for use with different vessels and applications. For example, European Patent EP 0593767, Swiss Patent CH241194 or U.S. Pat. No. 2,331,234 disclose filter systems which are inserted into a vessel such as a tube so that the filter flange is supported by the opening of the vessel. In other words, the filter systems hangs inside the tube, which means that this filter system only works with the tube size it is designed for.
A similar filter system is disclosed in International Patent Publication WO 2009/096790 A1, where the filter is provided with a plurality of supporting edges which fit to the outside of a vessel. The filter rests via the supporting edges on the vessel. Filters in the prior art simply sitting on top of a vessel (tube) tend to tilt over.
Filters in the prior art hanging inside a vessel (tube) leave essentially no space between the side walls of the filter and the vessel, which impairs venting when the filter is filled with liquid (e.g., a suspension). The result is a “flow stop”, especially if a slightly viscous sample is processed, and then the filter needs to be lifted up manually to clear it. The filter area is provided in a frame with a grip handle in order to handle the filter and preserve aseptic conditions without touching the filter's sieve area. However, the grip handle is quite small and difficult to handle under the usual working conditions in a laboratory. Furthermore, the volume of the filter system above the sieve is too small to hold the sample volume of a standard tube, which makes refilling necessary if liquid does not run through the sieve immediately during pipetting.
Furthermore, filter systems designed for laboratory vessels having a small volume are usually of small size with a small filter area. Small filter areas tend to clog and/or their processing speed is rather low. On the other hand, use of tubes with a smaller diameter has clear advantages in reduced wash volumes, rack space, higher number of samples to be processed with a centrifuge and better pellet formation after centrifugation.
Accordingly there is a need for a filter system which provides sufficient filter efficiency but is also compatible with small tube sizes.